1. Field of the Invention
The invention relates to a translucent protective element having at least two support elements, for example glass plates, and an intumescent fire protection layer in an intermediate space between the support elements.
2. Description of Related Art
Such protective elements are known, for example, from EP 0 620 781. The fire protection layer taught in this document is an aqueous alkali metal silicate which is produced by hardening of a water-containing filler composition composed of an alkali metal silicate and a hardener to form a polysilicate. The polysilicate has a molar ratio of silicon dioxide to alkali metal oxide of at least 4:1. The fully hardened fire protection layer contains essentially all the water of the water-containing filler composition due to hardening taking place in the sealed intermediate space between the support elements. The water content is in the range from 44 to 60 percent by weight. The heat protection element produced in this way has excellent fire protection properties and can be produced in a rational process.
An alternative process for producing a fire protection layer is known, for example, from FR 2 607 491 or from WO 2007/118887. This alternative process provides for an alkali metal silicate layer to be poured in the liquid state onto a glass plate and subsequently be dried, with the fire protection layer remaining on the glass plate during use and in the final state having a comparatively low water content in the range from, for example, 22% to 35% (% by weight). The second glass plate is adhesively bonded to the fire protection layer after the drying process. The alternative process has the disadvantage that the physical drying process takes a long time, which makes production of the heat protection element considerably more expensive.
Fire protection layers, according to the prior art, thus generally have a relatively high liquid content, which can result in the fire protection layer having a residual flowability. Reducing the water content of the starting materials for mixing of the filler composition, i.e. the use of more highly concentrated raw materials, is often not feasible since solutions collapse at an excessively high solids content and precipitates occur. This applies, for example, to potassium silicate and silica sol or to potassium hydroxide and a slurry of pyrogenic silica. Degassing the filler composition in the mixing vessel, which also results in water being given off, before introduction into the intermediate space is also known from EP 0 620 781 or EP 1 399 314. However, the amount of water which can be taken off in this way is very small since the filler composition must not be heated in the mixing vessel and exposed to the evaporation process to such an extent or time that hardening commences or proceeds too far. After introduction into the intermediate space, virtually no more water can be removed because the intermediate space has to be hermetically sealed during the chemical hardening of the silicate composition.